Document scanners convert a visible image on a document, photograph, a transparent media and the like into an electronic form suitable for copying, storing and processing by a computer. A document scanner may be a stand-alone device or integrated with a copier, a facsimile machine, a multipurpose device, a printer or another imaging apparatus.
Scanners are typically stationary devices which have a transparent plate or platen against which an object to be scanned, such as a paper document, is placed. The document is scanned by sequentially imaging narrow strips, or scan lines, of the document using an optical sensor or photosensitive element such as a charge coupled device (CCD) array. The optical sensor produces electronic data which is representative of each scan line.
In one type of scanner, the current scan line portion of the document which is imaged on the sensor array is changed, or “swept,” by moving the platen supporting the document relative to the scanner imaging assembly. In another type of scanner, the platen and document remain stationary and at least a portion of an imaging assembly is moved to change the scan line portion which is currently imaged. An automatic document feeder (ADF) device may also be integrated with a scanner which sequentially moves documents across a portion of the scanner platen.
Scanner systems featuring an ADF provide scanning of dual-sided media by imaging a first side of a document during a first passage of the document across the scanner platen and subsequently reversing, or flipping, the document and imaging a second side of the document during a second document passage across the scanner platen. Scanner systems featuring an ADF may also be configured to automatically detect and initiate duplex scanning operations when an image is detected on both sides of a document.
Some scanning systems configured to automatically detect and initiate duplex scanning operations comprise secondary sensors or photosensitive elements incorporated into the ADF to determine whether an image resides on the back surface of the document. Based on data acquired by the secondary sensors, the scanning system may be configured to automatically initiate duplex scanning if a back surface image is detected. However, incorporating additional sensing or photosensitive elements into the ADF generally increases the manufacturing cost associated with the scanning system. Additionally, integrating the secondary photosensitive elements with the assortment of rollers and document feed paths to obtain duplex scanning operations is complex and time-consuming.